1. Field of the Invention
This invention relates generally to wireless nodes and, more particularly, to battery powered wireless nodes for systems, such as, for example, a wireless local area network (WLAN) or a low rate—wireless personal area network (LR-WPAN). The invention also relates to systems employing battery powered wireless nodes.
2. Background Information
Wireless communication networks are an emerging new technology, which allows users to access information and services electronically, regardless of their geographic position.
All nodes in ad-hoc networks are potentially mobile and can be connected dynamically in an arbitrary manner. All nodes of these networks behave as routers and take part in discovery and maintenance of routes to other nodes in the network. For example, ad-hoc networks are very useful in emergency search-and-rescue operations, meetings or conventions in which persons wish to quickly share information, and in data acquisition operations in inhospitable terrains.
An ad-hoc mobile communication network comprises a plurality of mobile hosts, each of which is able to communicate with its neighboring mobile hosts, which are a single hop away. In such a network, each mobile host acts as a router forwarding packets of information from one mobile host to another. These mobile hosts communicate with each other over a wireless media, typically without any infra-structured (or wired) network component support.
In contrast to wired networks, mesh-type, low rate—wireless personal area network (LR-WPAN) wireless communication networks are intended to be relatively low power, to be self-configuring, and to not require any communication infrastructure (e.g., wires) other than power sources.
Relatively low power, radio frequency (RF) lighting control systems employ wall-mounted, battery powered, RF switch “sensors”. Such a sensor sends a signal to a remote power control device, such as relay, in order to turn one or more house lights on and off.
U.S. Patent Application Publication No. 2004/0028023 discloses an asynchronous event driven sensor network. That is, sensors are activated by external events that will occur in an asynchronous manner. Thus, the sensors will typically transmit data asynchronously. All nodes remain silent, except for a background inquiry scan process, unless an event occurs. This minimizes power consumption and minimizes the probability of detection.
U.S. Patent Application Publication No. 2004/0100394 discloses that when wireless nodes are powered by battery power or solar power, power conservation is important. To conserve power, the transceivers in the wireless nodes can remain powered down. However, to restore end-to-end network connectivity, the nodes must all be active so that messages can be forwarded through the nodes. In normal operation, the system causes the transceivers of all the wireless nodes to power down. Then, when messages are to be transmitted, a synchronization event is used to synchronously bring all nodes out of a powered down state. The synchronization event can be time based, such as a particular period or duration agreed to before the nodes are powered down. After a pre-defined period or the receipt of a power-down message, the wireless nodes will power down. Any pair of wireless nodes that want to communicate with each other can schedule a time slot on an ad hoc basis, depending on the response time requirements of the application. During the communication between a pair of nodes, the nodes determine the start time of the next communication time so that the nodes do not have to use power with their receivers or transmitters on until the next scheduled transmission time. The nodes can turn the power off to the transceiver until the next scheduled transmission time. To further reduce power requirement, wireless nodes should maintain reasonably accurate time bases so that transmissions can be synchronized.
U.S. Patent Application Publication No. 2005/0096101 discloses a display and a slave application that displays information received from a supermarket information server when it passes near a transceiver.
There is room for improvement in battery powered wireless nodes. There is also room for improvement in systems employing battery powered wireless nodes.